Field of the Invention
The present invention relates to a rotation driving apparatus which comprises a transmission driven by a rotation driving source, and an output-side sensor for obtaining a rotation angle of the output-side rotation shaft of the transmission, a robot apparatus which uses the rotation driving apparatus, a control program which is used for the rotation driving apparatus, and an article manufacturing method which is performed by the robot apparatus.
Description of the Related Art
In recent years, a producing (manufacturing) apparatus in which a multi-joint robot (simply called a robot hereinafter) is used becomes widespread in the field of industrial manufacturing. Here, the robot comprises, for example, a plurality of joints each driven by a rotation driving apparatus and thus enables to achieve complicated and high-speed article manufacturing work as with human hands. In the robot like this which can perform such complicated operations, since a degree of freedom of the operation by a robot arm is high, there is a possibility that the robot arm comes into contact with another object such as a workpiece, a tool or the like in a surrounding environment while the manufacturing work is being performed. Thus, for example, if the robot arm comes into contact with a peripheral object or the like and thus a transmission (speed reducer) disposed in the joint of the arm is subject to impact, there is a fear that a breakdown (trouble) such as tooth skipping (tripping) or the like occurs in the speed reducer.
Here, an actuator which is used to drive the rotation driving apparatus being the joint of the robot arm of this type is constituted by, for example, a servo motor and a transmission. In general, the transmission of this type is often constituted as a speed reducer because of relation of a rotation speed region of a rotation driving source such as the servo motor and a rotation speed region for rotating a link of the arm. For this reason, in the following, the speed reducer might exemplarily be described as a representative of the transmission to be used in the robot of this type.
As the relevant transmission, a transmission which uses a strain wave gearing mechanism by which a large speed reduction ratio can be obtained as compared with size and shape is widely used. In the transmission (speed reducer) which uses the relevant strain wave gearing mechanism, since angle transmission accuracy of the joint deteriorates due to a breakdown such as tripping or the like, there is a possibility that operation accuracy of the robot arm resultingly deteriorates.
In consideration of such circumstances as above, various techniques related to an interference and a collision of the robot arm are recently proposed. For example, the technique of providing an angle detector at each of the input and output sides of the actuator (motor and transmission) of each joint (each rotation driving apparatus) of the robot arm is proposed (Japanese Patent Application Laid-Open No. 2010-228028). More specifically, in the relevant technique, it is decided based on a detected angle difference between the input and output sides of the actuator whether or not a collision occurs, and, when it is decided that the collision occurs, the robot arm is driven in the reverse direction. Besides, the technique of detecting the state of the actuator (motor and transmission) of the joint after an interference or a collision of the arm occurred is widely known. For example, the technique of detecting a vibration of the arm at the time of driving the actuator of each joint by using a torque variation value calculated based on the motor torque value, comparing such a variation width with a threshold, and, based on the comparison result, deciding whether or not to exchange the necessary part is proposed (Japanese Patent Application Laid-Open No. 2006-281421).
In the technique disclosed in Japanese Patent Application Laid-Open No. 2010-228028, it is possible to detect that contact occurs at the robot arm. However, since it is difficult to visually confirm the transmission externally, it is substantially impossible to know the degree of damage of the transmission occurred by the contact. For this reason, to know or grasp the damage of the transmission, it is necessary to confirm the tooth plane of the gear by dismantling the transmission itself, and then decide whether or not exchange of the part(s) is necessary. Here, when knowing the damage by dismantling the transmission, it is necessary to remove the transmission from the robot arm, and thus there is a problem that it takes a lot of time to do so. On the other hand, in the technique disclosed in Japanese Patent Application Laid-Open No. 2006-281421, since the value to be used for abnormality detection is obtained from the motor torque value, there is a problem that it is impossible to sufficiently obtain high detection accuracy because of the influence of the servo responsiveness of the arm itself.